1. Field of the Invention
The present invention relates to a method and apparatus for controlling a force assist apparatus used for nursing and rehabilitation tasks in hospitals and homes, and for the conveyance of heavy objects such as in the manufacturing, mining, agriculture, fisheries, construction and distribution industries.
2. Description of the Prior Art
Exoskeleton force assist apparatuses that are worn by an operator to attenuate a load force applied to the operator include apparatuses developed in the 1960s by General Electric of the United States, and the systems being researched since the latter part of the 1980s by Kazerooni of the University of California at Berkeley. In each of these, a load force exerted on the apparatus is attenuated by a fixed factor and applied to the operator. The aim of these conventional apparatuses is to help an operator to accomplish a heavy-duty task by amplifying his/her force by a very high degree. However, a problem with these systems are that the safety of the operator cannot be fully ensured in an emergency stop of the apparatus. This problem arises because the apparatus is used in an attempt to accomplish a heavy-duty task that cannot be done by a human alone.
At various operation sites, such as in rehabilitation care and the like, it may be that while an unaided human may be able to accomplish a task, the task imposes an excessive load on the human and may be difficult to carry out continuously over an extended period of time. In such cases, applying a force assist apparatus is not only effective for reducing the load on the operator, but can also ensure the safety of operators, since the load is not so large, even in an emergency stop of the apparatus. In such a case, however, with no heavy-duty operation being involved, there is a need for an apparatus that is lighter and more compact than the conventional arrangements. For this, a force assist arrangement is required that uses compact actuators which have a smaller torque or force output.
However, when actuators are reduced in size and used at near the limit of their torque/force output capability, there is a risk that during operation the actuators will reach the limit of their output and become saturated. When actuators become saturated, the apparent force attenuation factor rapidly deteriorates and the ratio of the assist force undergoes unpredictable, discontinuous changes, impeding smooth operation and actually causing operator fatigue. With the type of conventional apparatus described above, the only way around this problem is to increase the attenuation factor itself. While doing this enables actuator saturation to be circumvented, it reduces the force assist effect and limits the types of tasks that can be accomplished.
The object of the present invention is to provide a method and apparatus for controlling a force assist apparatus that, with respect to small-output actuators, does not give rise to actuator saturation and does not reduce the force assist effect.